Unit test for binomial_cdf
Fixed gradients and vectorization
Unit tests for Bernoulli CDF
Gradient and vectorization fixes
Tweaked invalid values
Fixed boundary value behavior
Unit test for negative binomial CDF.  Still need to implement cdf_function properly.
Fixed implementation and vectorization.  Stability of grad2F1 (used by gradIncBeta from gradRegIncBeta) fragile for large n -- need to fix?
Unit tests for Beta-Binomial CDF
Fixed implementation and vectorization
In 3F2 and grad3F2, loop until desired precision instead of set number of iterations